Double synthetic antiferromagnet using rare earth metals and transition metals

ABSTRACT

A mechanism relates to magnetic random access memory (MRAM). A free magnetic layer is provided and first fixed layers are disposed above the free magnetic layer. Second fixed layers are disposed below the free magnetic layer. The first fixed layers and the second fixed layers both comprise a rare earth element.

PRIORITY

This application is a continuation of and claims priority from U.S.patent application Ser. No. 14/584,001, filed on Dec. 29, 2014, entitled“DOUBLE SYNTHETIC ANTIFERROMAGNET USING RARE EARTH METALS AND TRANSITIONMETALS”, the entire contents of which are incorporated herein byreference.

BACKGROUND

The present invention relates to magnetic random access memory (MRAM),and more specifically, to using rare earth and transition metals inreference and dipole layers.

A spin torque magnetic random access memory (MRAM) device uses a twoterminal spin-torque based memory element. The two terminal spin-torquebased memory element includes a pinned layer, a tunnel barrier layer,and a free layer in a magnetic tunnel junction (MTJ) stack. The pinnedlayer is also called the reference layer. The magnetization of thepinned layer is fixed in a direction such that when current passesthrough the MTJ stack the free layer becomes either parallel oranti-parallel to the pinned layer. Resistance of the device depends onthe relative orientation of the free layer and the pinned layers.

SUMMARY

According to one embodiment, a magnetic random access memory (MRAM)device is provided. A free magnetic layer is provided, and first fixedlayers are disposed above the free magnetic layer. Second fixed layersare disposed below the free magnetic layer. The first fixed layers andthe second fixed layers both comprise a rare earth element.

According to one embodiment, a method of forming a magnetic randomaccess memory (MRAM) device is provided. The method includes providing afree magnetic layer, disposing first fixed layers above the freemagnetic layer, and disposing second fixed layers below the freemagnetic layer. The first fixed layers and the second fixed layers bothcomprise a rare earth element.

According to one embodiment, a magnetic random access memory (MRAM)device is provided. The MRAM device includes a free magnetic layer, afirst synthetic antiferromagnet (SAF) above the free magnetic layer, atunnel barrier sandwiched between the free magnetic layer and the firstsynthetic antiferromagnet, a second synthetic antiferromagnet below thefree magnetic layer. The first synthetic antiferromagnet and the secondantiferromagnet both comprise a rare earth element. An oxide layer issandwiched between the free magnetic layer and the second syntheticantiferromagnet.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a magnetic random access memory (MRAM) device;

FIG. 2 illustrates a magnetic random access memory (MRAM) deviceaccording to an embodiment;

FIG. 3 is a graph illustrating the magnetic dipole field created by thedouble synthetic antiferromagnet (SAF) in the MRAM device according toan embodiment;

FIG. 4 is a graph illustrating the magnetic dipole fields created by thedouble synthetic antiferromagnet (SAF) compared to a single SAFaccording to an embodiment;

FIG. 5 illustrates a method of forming a magnetic random access memory(MRAM) device according to an embodiment; and

FIG. 6 illustrates an example computer that can implement and includefeatures discussed herein according to an embodiment.

DETAILED DESCRIPTION

Spin torque MRAM requires that the magnetic tunnel junction (MTJ) stackhas a well-centered hysteresis loop with zero offset field. The dipolefield emanating from the reference layers acts on the free layer andoffsets the free layer hysteresis loop so that it is not centered onzero field. When the free layer hysteresis loop is not well centered theactivation energy, required for data retention, is reduced.State-of-the-art techniques require using a synthetic antiferromagnetcontaining a 0.4 nanometer (nm) ruthenium (Ru) spacer, which isdifficult to manufacture. If a dipole layer uses a rare-earth metal inthe state of the art, there is no way to set the (magnetic moment)dipole layers in the correct direction reliably.

According to an embodiment, a spin torque MRAM device can use two (ormore) rare-earth and transition metal multilayers. The two rare earthand transition metal multilayers include one layer as a reference layer(in which the reference layer contains a thin nonmagnetic spacer such asa tantalum (Ta) nonmagnetic spacer) and one layer as a dipole layer.Although tantalum may be utilized as one option, the nonmagnetic spacerlayer does not need to be made from tantalum. The nonmagnetic spacer mayalso be made from niobium (Nb), tungsten (W), molybdenum (Mo), zirconium(Zr), and/or any other non-magnetic material. The thin Ta nonmagneticspacer is not required to be continuous (i.e., the material may haveholes in it) and thus is easily manufacturable. Although in oneimplementation, the Ta nonmagnetic spacer may be continuous if desired.The nonmagnetic spacer enables the coercivity, Hc, of the referencelayer to be tuned to a low value. However, the dipole layer has a verylarge coercivity Hc. In this way, there is a large window between the Hcof the reference layer and Hc of the dipole layer, so that every bit canbe set correctly.

In materials science, the coercivity (Hc), also called the coercivefield or coercive force, is a measure of a ferromagnetic material towithstand an external magnetic field. The coercivity is the amount ofmagnetic field required to switch the magnetic moment of the referencelayer and dipole layer, respectively.

Now turning to the figures, FIG. 1 illustrates a magnetic random accessmemory (MRAM) device 100. As shown in FIG. 1, MRAM device 100 includes areference layer 125 (also referred to as a pinned magnetic layer), atunnel barrier layer 120, and a free magnetic layer 115 adjacent to thetunnel barrier layer 120. The reference layer 125, tunnel barrier layer120, and free magnetic layer 115 form a magnetic tunnel junction (MTJ)stack.

The MRAM device 100 also includes an oxide seed 110 adjacent to the freemagnetic layer 115 and a dipole magnetic layer 105 adjacent to the freemagnetic layer 115. The oxide seed 110 helps to make the free magneticlayer 115 have perpendicular magnetization.

The reference magnetic layer 125 may be formed of iron platinum (FePt)or iron palladium (FePd). The reference magnetic layer 125 may be formedof at least one of platinum (Pt) or palladium (Pd), and at least one ofcobalt iron CoFe or cobalt (Co). The tunnel barrier layer 120 may beformed of magnesium oxide (MgO). The oxide seed 110 may be formed ofMgO. The dipole magnetic layer 105 may be almost identical to thereference magnetic layer 125, in order to cancel out the stray field(exhibited upon the free magnetic layer 115).

The magnetic moment of the reference magnetic layer 125 is shown by adownward pointing arrow. The magnetic moment of the dipole magneticlayer 105 is shown by an upward pointing arrow, which means the strayfields caused by the magnetic moments of the dipole layer 105 andreference layer 125 are intended to cancel out one another. The magneticmoment of the free magnetic layer 115 is shown by a double arrowindicating that the magnetic moment can be switched either up or downaccording to the direction of an applied current from the voltage source130. The magnetic moments of the reference, free, and dipole layers areall perpendicular to the plane of MRAM device 100.

The free magnetic layer 115 has a magnetic moment that is eitherparallel or anti-parallel to the magnetic moment of the pinned referencemagnetic layer 125. The tunnel barrier layer 120 is thin enough that acurrent through it can be established by quantum mechanical tunneling ofconduction electrons. The resistance of the free magnetic layer 115changes in response to the relative orientation between the freemagnetic layer 115 and the reference magnetic layer 125. For example,when a current (i) passes down through the MTJ stack in a directionperpendicular to the MTJ stack layers, the magnetic moment of the freemagnetic layer 115 is rotated parallel to the reference layer 125 (i.e.,“1” memory state), resulting in a lower resistance. When a current (i)is passed up through the MTJ stack, the magnetic moment of the freemagnetic layer 115 is rotated antiparallel to the reference layer 125(i.e., “0” memory state), resulting in a higher resistance.

In the state of the art, there are not materials utilized that givelarge enough Hc (e.g., Hc>2000 oersted (Oe)), and that provide a largeenough window between the Hc of the reference magnetic layer 125 and theHc of the dipole layer 105.

It might be desirable to have one He small such as approximately (˜) 3kiloOe (kOe) and to have the other He large such as approximately (˜) 15kOe according to an embodiment (shown in FIG. 2). This would provide alarge window or large difference (15-3 kOe=12 kOe) between the requiredswitching field coercivity (Hc) of the reference magnetic layer (250) asopposed to the dipole magnetic layer (260) according to an embodiment.

Assume that the He of the reference layer is higher than the He of thedipole layer. To set the magnetic moments of both the reference layer125 and the dipole layer 105, a large magnetic field at least equal tothe larger He of the reference layer is applied downward on the MRAMdevice 100 to set the magnetic moments of both the reference layer 125and the dipole layer 105 down. If the He of the reference layer 125 is 1kOe and the He of the dipole layer 105 is 0.5 kOe, then the largemagnetic field to set the magnetic moments is at least 1 kOe. As such,this large magnetic field (of, e.g., 1 kOe) switches both magneticmoments down.

To set the magnetic moment of the dipole layer 105 upward, a smallermagnetic field pointing up is applied. This smaller magnetic field is tobe at least 0.5 kOe (but less than 1 kOe) to switch the magnetic momentof the dipole layer 105 (with He of 0.5 kOe) but not the reference layer125 (requiring He of 1 kOe). However, in the state of the art, the He ofthe reference and dipole layers may not always be exactly the same forall junctions, and so there is not a large window between/separating therespective He of reference and dipole layers. When using the smallermagnetic field of 0.5 kOe to set the dipole magnetic layer 105 (havingHe=0.5 kOe), the magnetic moment of the reference layer 125 mayinadvertently be set on some of the junctions in the memory arraybecause of the small window between the He of the reference layer 125and the dipole layer 105. As understood by one skilled in the art, thereare multiple MRAM devices connected in an array.

According to an embodiment, FIG. 2 illustrates a magnetic random accessmemory (MRAM) device 200. The MRAM device 200 has the tunnel barrierlayer 120, free magnetic layer 115, and oxide seed 110 as discussed inFIG. 1. Additionally, MRAM device 200 includes reference magneticlayer_2 220 adjacent to a nonmagnetic spacer layer 225, and a referencemagnetic layer_1 215 adjacent to both the nonmagnetic spacer 225 and thetunnel barrier layer 120. On the other side of the free magnetic layer115, a dipole magnetic layer_1 210 is adjacent to the oxide seed layer110, and a dipole magnetic layer_2 205 is adjacent to the dipole layer_1210.

The reference layer_1 215 and the reference layer_2 220 have oppositepointing magnetic moments and together form a synthetic antiferromagnet(SAF). The combination (and combined effect) of reference layer_1 215and the reference layer_2 220, along with the nonmagnetic spacer 225acts as a single reference magnetic layer 250. The reference magneticlayer 250 has its own Hc, which is the combined effects of the Hc forreference magnetic layer_1 215 and reference magnetic layer_2 220 (asreduced by the nonmagnetic spacer 225).

The dipole magnetic layer_1 205 and the dipole magnetic layer_2 210 haveopposite magnetic moments and together form a synthetic antiferromagnet(SAF). The combination (and combined effect) of dipole magnetic layer_1205 and the dipole magnetic layer_2 210 acts as a single dipole magneticlayer 260. The dipole magnetic layer 260 has its own Hc, which is thecombined effects of the Hc for the dipole magnetic layer_1 210 anddipole magnetic layer_2 205.

In FIG. 2, the dipole magnetic layer_1 210, dipole magnetic layer_2 205,reference magnetic layer_1 215, reference magnetic layer_2 220 are allmade out of rare-earth metal and transition metal multilayers and/orrare-earth metal and transition-metal alloys. For example, therare-earth metal and transition-metal alloy may be CoFeTb. In anotherexample, the rare-earth metal and transition-metal multilayers mayinclude one or more alternating layers of a layer of CoFe, a layer ofTb, a layer of CoFe, a layer of Tb, and so forth.

A rare earth element (REE) (or rare earth metal) is one of fourteen rareearth elements composed of the lanthanide series. The rare earth metalsare found in group 3 of the periodic table, and the 6th period. Rareearth elements in the lanthanide series include cerium, praseodymium,neodymium, promethium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Terbium(Tb) and gadolimium (Gd) work better than other rare earth elements,since Tb and Gd provide more perpendicular magnetic anisotropy.

The transition metals which are ferromagnetic at room temperatureinclude iron, cobalt, and nickel.

Use of the nonmagnetic spacer 225 (e.g., 2 angstroms (Å) of Ta) in thereference magnetic layer 250 (which is utilized to increase magnetoresistance (MR)) creates a low direct write field (Hd) for the referencemagnetic layer 250, such as Hc is approximately (˜) 3 kOe. Note that ina special case the direct write field Hd of reference magnetic layer 250is equal to Hc, such that Hd=Hc=3 kOe for the reference magnetic layer250. The dipole magnetic layer 260 does not include the Ta nonmagneticspacer, so the dipole magnetic layer 260 has a very large Hc (incomparison to the reference magnetic layer 250), such as Hc 15 kOe. Thisdifference in Hc (between the dipole and reference layers) allows enoughmargin to set the directions for the magnetic moments for both thedipole magnetic layer 260 and reference magnetic layer 250. To set theMRAM device 200, first apply a positive field of more than 15 kOe to setthe magnetization of both dipole layer 1 and reference layer 1 pointingup. Then apply a field between 3 and 15 kOe, for example 9 kOe, toreverse only the reference layer 1 (make it point down), while leavingthe dipole layer 1 pointing up.

According to an embodiment, the Hc (e.g., 3 kOe) of the referencemagnetic layer 250 maintains the same relationship as a function oftemperature to the Hc (e.g., 15 kOe) of dipole magnetic layer 260because the same materials are utilized in both the reference magneticlayer_1 215 and the dipole magnetic layer_1 210 and the same materialsare utilized in both reference magnetic layer_2 220 and dipole magneticlayer_2 205. Also, the Hc of the reference magnetic layer 250 and the Hcof dipole magnetic layer 260 have a large window of separation betweenthe two, and the He of the reference magnetic layer 250 and the He ofdipole magnetic layer 260 both change in the same manner withtemperature.

The reference magnetic layer_1 215, the reference magnetic layer_2 220,the dipole magnetic layer_1 210, and the dipole magnetic layer_2 205each has its own magnetic moment pointing in a respective direction.Each individual magnetic moment (in the reference magnetic layer_1 215,the reference magnetic layer_2 220, the dipole magnetic layer_1 210, andthe dipole magnetic layer_2 205) creates/generates a dipole field.Dipole fields, sometimes referred to as stray fields, can act upon thefree magnetic layer 115. The dipole fields (corresponding to respectivemagnetic moments) created by the reference magnetic layer_1 215, thereference magnetic layer_2 220, the dipole magnetic layer_1 210, and thedipole magnetic layer_2 205 are configured to cancel each other out atthe position of the free layer; this cancellation of the dipole fields(that affect the free magnetic layer 115) is because of the constructionof equal and opposite dipole fields in reference magnetic layer 250 anddipole magnetic layer 260.

Cancellation of dipole fields happens between reference magnetic layer_2220 and the dipole magnetic layer_2 205. Particularly, the dipole fieldof the reference magnetic layer_2 220 is cancelled out by the dipolefield of the dipole magnetic layer_2 205. The reference magnetic layer_2220 and the dipole magnetic layer_2 205 are made of the same material(such as, e.g., Co, Fe, and Tb in one case, or Co, Fe, and Gd in anothercase) and have the same thickness (in the z axis) but have magneticmoments in the opposite directions. Having magnetic moments in oppositedirections allows for dipole fields in the opposite direction, thuscancelling the dipole field (or stray field) effect on the free magneticlayer 115 from reference magnetic layer_2 220 and the dipole magneticlayer_2 205.

Similarly, cancellation of dipole fields happens between referencemagnetic layer_1 215 and the dipole magnetic layer_1 210. Particularly,the dipole field of the reference magnetic layer_1 215 is cancelled outby the dipole field of the dipole magnetic layer_1 210. The referencemagnetic layer_1 215 and the dipole magnetic layer_1 210 are made of thesame material (such as, e.g., Co, Fe, and Tb in one case, or Co, Fe, andGd in another case) and have the same thickness (in the z axis), buthave magnetic moments in the opposite directions. Having magneticmoments in opposite directions allows for dipole fields in the oppositedirection, thus cancelling the dipole field (or stray field) effect onthe free magnetic layer 115 from reference magnetic layer_1 215 and thedipole magnetic layer_1 210.

In a typical MRAM device, the operational temperature may change frombetween 0-85° Celsius (C), which causes a change in the magnitude of themagnetic dipole field, along with a change in Hc. However, since thematerial and thickness are identical in both the reference magneticlayer_1 215 and the dipole magnetic layer_1 210, the magnitudes of theirrespective dipole fields change in the same amount (i.e., change in thesame values). For example, when the magnitude of the dipole field forreference magnetic layer_1 215 increases because of a change intemperature, the magnitude of the dipole field for the dipole magneticlayer_1 210 increases in the same amount. This also occurs when themagnitudes decrease because of a change in temperature.

Similarly, since the material and thickness are identical in both thereference magnetic layer_2 220 and the dipole magnetic layer_2 205, themagnitudes of their respective magnetic dipole fields change in the sameamount (i.e., change in the same values). For example, when themagnitude of the dipole field for reference magnetic layer_1 215increases because of a change in temperature, the magnitude of thedipole field for the dipole magnetic layer_1 210 increases in the sameamount. This also occurs when the magnitudes decrease because of achange in temperature.

Accordingly, the reference magnetic layer_1 215 and the dipole magneticlayer_1 210 have equal magnitudes and opposite dipole field directions,where their magnitudes have the same temperature dependence. Likewise,the reference magnetic layer_2 220 and the dipole magnetic layer_2 205have equal magnitudes and opposite dipole field directions, where theirmagnitudes have the same temperature dependence. This means anytemperature dependence of the reference magnetic layer_1 215 and thedipole magnetic layer_1 210 is automatically compensated for. Similarly,any temperature dependence of the reference magnetic layer_2 220 and thedipole magnetic layer_2 205 is automatically compensated for.

The reference magnetic layer_1 215 may have a thickness (in the z-axis)ranging from 1 nm to 10 nm and likewise the dipole magnetic layer_1 210may have a thickness (in the z-axis) ranging from 1 nm to 10 nm. Thereference magnetic layer_2 220 may have a thickness (in the z-axis)ranging from 1 nm to 10 nm, and similarly the dipole magnetic layer_2205 may have a thickness (in the z-axis) ranging from 1 nm to 10 nm.

FIG. 3 is a graph 300 illustrating the magnetic dipole field created bythe double synthetic antiferromagnet (SAF) (reference magnetic layer_2220 and reference magnetic layer_1 form the first SAF while dipolemagnetic layer_1 210 and dipole magnetic layer_2 205 form the secondSAF) and exhibited (felt) on the free magnetic layer 115 in the MRAMdevice 200 according to an embodiment. The magnetic dipole field for thedouble SAF is plotted as waveform 305. In FIG. 300, the y-axis shows themagnetic dipole field as Hz (Oe), which means that the magnetic dipolefield was measured in the z direction in FIG. 2. Although the magneticdipole field may flow in more than the z-axis direction (such as x-axisand y-axis), for purposes of the graph 300 (along with graph 400), thegraph 300 illustrates how the magnetic dipole field H_(z) acts upon thefree magnetic layer 115 in the z-axis direction.

In the graph 300, the x-axis illustrates the radial coordinate in themiddle of the free magnetic layer 115. In this example, assume that thediameter of the MRAM device 200 is about 30 nanometers (nm), andtherefore the diameter of the free magnetic layer 115 is about 30 nm.Considered from a cross-sectional view point as shown in FIG. 2, thecenter of the free magnetic layer 115 is to have the radial coordinate0. When starting from the center, moving to the right in the x-axisdirection traverses from 0 nm to 15 nm, and moving to the left traversesfrom 0 nm to −15 nm (where −15 nm means traversing the oppositedirection along the free magnetic layer 115).

For the calculation in graph 300 in FIG. 3, the tunnel barrier layer 120is made of MgO and has a thickness of 1 nm, the free magnetic layer 115is made of CoFeB and has a thickness of 2 nm, the oxide seed layer 110is made of MgO and as a thickness of 1 nm, the reference magneticlayer_2 220 is made of CoFeTb, has a thickness of 10 nm, and has asaturation magnetization Ms=800 emu/cm³ (where emu is theelectromagnetic unit), and the nonmagnetic spacer 225 is made of Ta andhas a thickness of 0.2 nm.

Also, for the experiment in graph 300 in FIG. 3, the reference magneticlayer_1 215 is made of CoFe, has a thickness of 1.5 nm, and has asaturation magnetization of Ms=800 emu/cm³, the dipole magnetic layer_1210 is made of CoFe, has a thickness of 1.5 nm, and has a magnetizationof Ms=800 emu/cm³, and dipole magnetic layer_2 205 is made of CoFeTb,has a thickness of 10 nm, and has a magnetization Ms=800 emu/cm³.

As can be seen in graph 300, the double SAF (in MRAM 200) causes twopeaks in the magnetic dipole field (as felt by the free magnetic layer115 near −10 nm and 10 nm), and the two peaks are slightly below 5 Oe(Hz˜5 Oe). Also, the double SAF (in MRAM 200) causes a dip in the dipolefield at 0 nm (center) of the free magnetic layer 115, and the dip doesnot reach −5 Oe (Hz˜−5 Oe).

The MRAM device 200 (because of the double SAF, i.e., reference magneticlayer 250 and dipole magnetic layer 260) has almost zero local magneticdipole field (i.e., at each respective radial coordinate) and almostzero average magnetic dipole field on the free magnetic layer 115. Theaverage magnetic dipole field is less than 5 Oe.

FIG. 4 is a graph 400 illustrating a waveform 405 as the magnetic dipolefield created by a single SAF in an MRAM device and the waveform 305 asthe magnetic dipole field created by double SAF in the MRAM device 200(discussed in FIG. 3).

In FIG. 4, the single SAF (in a similar MRAM to MRAM 200 but withoutdipole magnetic layer_1 210 and dipole magnetic layer_2 205) causes twopeaks in the dipole field (as felt by the free magnetic layer near −10nm and 10 nm), and the two peaks are approximately 300 Oe (Hz˜300 Oe).Also, the single SAF causes a dip in the dipole field at 0 nm (center)of the free magnetic layer, and the dip is approximately −300 Oe(Hz˜−300 Oe).

As compared to the single waveform 405, the double SAF waveform 305 hasvery little magnetic dipole field effect on the free magnetic layer 115.This small magnetic dipole field disturbs the free magnetic layer 115less, making free magnetic layer 115 switch more like a single magneticdomain.

Now turning to FIG. 5, a method 500 of forming a magnetic random accessmemory (MRAM) device 200 is provided according to an embodiment. Atblock 505, the free magnetic layer 115 is provided. At block 510, firstfixed layers (e.g., reference magnetic layer_1 215 and referencemagnetic layer_2 220) are disposed above the free magnetic layer 115. Atblock 515, second fixed layers (e.g., dipole magnetic layer_1 210 anddipole magnetic layer_2 205) are disposed below the free magnetic layer115. At block 520, the first fixed layers (e.g., reference magneticlayer_1 215 and reference magnetic layer_2 220) and the second fixedlayers (e.g., dipole magnetic layer_1 210 and dipole magnetic layer_2205) both comprise a rare earth element (e.g., one or more rare earthelements).

The first fixed layers (e.g., reference magnetic layer_1 215 andreference magnetic layer_2 220) and the second fixed layers (e.g.,dipole magnetic layer_1 210 and dipole magnetic layer_2 205) bothcomprise a transition metal in addition to the rare earth element. Thetransition metal includes at least one of Co, Fe, and Ni. The rare earthelement includes at least one of Tb, Gd, and/or europium (Eu).

The first fixed layers (e.g., reference magnetic layer 1 215 andreference magnetic layer_2 220) and the second fixed layers (e.g.,dipole magnetic layer_1 210 and dipole magnetic layer_2 205) comprise atleast one of CoFe and Tb multilayers and a CoFeTb alloy.

The first fixed layers and the second fixed layers comprise at least oneof CoFe and Gd multilayers and a CoFeGd alloy. The free magnetic layer115 is sandwiched between two oxide layers (e.g., the tunnel barrierlayer 120 and oxide seed layer 110). The free magnetic layer 115 isgrown on the oxide seed layer 110. One side of the free magnetic layer115 is adjacent to the oxide seed layer 110, and the another side of thefree magnetic layer 115 is adjacent to the tunnel barrier layer 120. Thefirst fixed layers (e.g., reference magnetic layer_1 215 and referencemagnetic layer_2 220) or the second fixed layers (e.g., dipole magneticlayer_1 210 and dipole magnetic layer_2 205) are adjacent to the tunnelbarrier layer 120. There may be a case when the layers above and belowthe free magnetic layer 115 are reversed.

At least one of the first fixed layers (e.g., reference magnetic layer_1215 and reference magnetic layer_2 220) and the second fixed layers(e.g., dipole magnetic layer_1 210 and dipole magnetic layer_2 205)comprises a nonmagnetic spacer layer 225. Although the dipole magneticlayer_1 210 and dipole magnetic layer_2 205 are not shown sandwichingthe nonmagnetic spacer layer 225, the nonmagnetic spacer layer 225 maybe included in the dipole magnetic layer 260.

FIG. 6 illustrates an example computer 600 that can implement featuresdiscussed herein. The computer 600 may include a plurality of spintorque MRAM devices 200 connected in a grid to form addressable memorycells. One skilled in the art understands how to connect spin torqueMRAM devices. The computer 600 may be a distributed computer system overmore than one computer. Various methods, procedures, modules, flowdiagrams, tools, applications, circuits, elements, and techniquesdiscussed herein may also incorporate and/or utilize the capabilities ofthe computer 600. Indeed, capabilities of the computer 600 may beutilized to implement and execute features of exemplary embodimentsdiscussed herein.

Generally, in terms of hardware architecture, the computer 600 mayinclude one or more processors 610, computer readable storage memory 620(which may include one or more MRAM devices 200, e.g., in an array), andone or more input and/or output (I/O) devices 670 that arecommunicatively coupled via a local interface (not shown). The localinterface can be, for example but not limited to, one or more buses orother wired or wireless connections, as is known in the art. The localinterface may have additional elements, such as controllers, buffers(caches), drivers, repeaters, and receivers, to enable communications.Further, the local interface may include address, control, and/or dataconnections to enable appropriate communications among theaforementioned components.

The processor 610 is a hardware device for executing software that canbe stored in the memory 620.

The computer readable memory 620 can include any one or combination ofvolatile memory elements (e.g., random access memory (RAM), such asdynamic random access memory (DRAM), static random access memory (SRAM),etc.) and nonvolatile memory elements (e.g., ROM, erasable programmableread only memory (EPROM), electronically erasable programmable read onlymemory (EEPROM), programmable read only memory (PROM), tape, compactdisc read only memory (CD-ROM), disk, diskette, cartridge, cassette orthe like, etc.). Note that the memory 620 can have a distributedarchitecture, where various components are situated remote from oneanother, but can be accessed by the processor(s) 610.

The software in the computer readable memory 620 may include one or moreseparate programs, each of which comprises an ordered listing ofexecutable instructions for implementing logical functions. The softwarein the memory 620 includes a suitable operating system (O/S) 650,compiler 640, source code 630, and one or more applications 660 of theexemplary embodiments.

The I/O devices 670 may include input devices (or peripherals) such as,for example but not limited to, a mouse, keyboard, scanner, microphone,camera, etc. Furthermore, the I/O devices 650 may also include outputdevices (or peripherals), for example but not limited to, a printer,display, etc. Finally, the I/O devices 670 may further include devicesthat communicate both inputs and outputs, for instance but not limitedto, a NIC or modulator/demodulator (for accessing remote devices, otherfiles, devices, systems, or a network), a radio frequency (RF) or othertransceiver, a telephonic interface, a bridge, a router, etc. The I/Odevices 670 also include components for communicating over variousnetworks, such as the Internet or an intranet. The I/O devices 670 maybe connected to and/or communicate with the processor 610 utilizingBluetooth connections and cables (via, e.g., Universal Serial Bus (USB)ports, serial ports, parallel ports, FireWire, HDMI (High-DefinitionMultimedia Interface), etc.).

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), astatic random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method of forming a magnetic random accessmemory (MRAM) device, comprising: forming a first dipole magnetic layerdirectly on top of a second dipole magnetic layer, wherein the first andsecond dipole magnetic layers have opposite pointing magnetic moments,the first and second dipole magnetic layers together forming a firstsynthetic antiferromagnet, wherein the first and second dipole magneticlayers comprise alternating layers of a rare-earth metal and atransition-metal multilayer, wherein the rare-earth metal is selectedfrom a group consisting of Tb and Gd, wherein the first and seconddipole magnetic layers together forming the first syntheticantiferromagnet have a first coercivity; forming an oxide seed layerdirectly on top of the first dipole magnetic layer; forming a freemagnetic layer directly on top of the oxide seed layer; forming a tunnelbarrier directly on top of the free magnetic layer; forming a firstreference magnetic layer directly on top of the tunnel barrier; forminga nonmagnetic spacer layer directly on top of the first referencemagnetic layer; and forming a second reference magnetic layer directlyon top of the nonmagnetic space layer, wherein the first and secondreference magnetic layers have opposite pointing magnetic moments, thefirst and second reference magnetic layers together forming a secondsynthetic antiferromagnet, wherein the first and second referencemagnetic layers are made of a same material as the first and seconddipole magnetic layers, wherein the first and second reference magneticlayers together forming the second synthetic antiferromagnet have asecond coercivity, wherein the first coercivity is greater than thesecond coercivity, wherein the first dipole magnetic layer and the firstreference magnetic layer have a same thickness ranging from 1-10nanometers, wherein the second dipole magnetic layer and the secondreference magnetic layer have a same another thickness ranging from 1-10nanometers, wherein when a magnitude of a dipole field for the firstreference magnetic layer increases because of a change in temperature amagnitude of a dipole field for the first dipole magnetic layerincreases in a same amount.